Lithographic apparatus and device manufacturing method

ABSTRACT

An immersion lithographic apparatus has adaptations to prevent or reduce bubble formation in one or more gaps in the substrate table by preventing bubbles escaping from the gap into the beam path and/or extracting bubbles that may form in the gap.

This is a continuation of U.S. patent application Ser. No. 15/470,491,filed Mar. 27, 2017, which is a continuation of U.S. patent applicationSer. No. 14/975,513, filed Dec. 18, 2015, now U.S. Pat. No. 9,606,449,which is a continuation application of U.S. patent application Ser. No.13/361,443, filed Jan. 30, 2012, now U.S. Pat. No. 9,229,335, which is acontinuation application of U.S. patent application Ser. No. 13/242,004,filed Sep. 23, 2011, now U.S. Pat. No. 9,081,300, which is acontinuation application of U.S. patent application Ser. No. 13/240,946,filed Sep. 22, 2011, now U.S. Pat. No. 9,146,478, which is acontinuation application of U.S. patent application Ser. No. 12/213,427,filed Jun. 19, 2008, now U.S. Pat. No. 8,115,903, which is a divisionalapplication of U.S. patent application Ser. No. 11/120,176, filed May 3,2005, now U.S. Pat. No. 7,433,016, the entire contents of each of theforegoing applications is hereby incorporated by reference.

FIELD

The invention relates to a lithographic apparatus and a method formanufacturing a device.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. The point of this is to enableimaging of smaller features since the exposure radiation will have ashorter wavelength in the liquid. (The effect of the liquid may also beregarded as enabling the use of a larger effective NA of the system andalso increasing the depth of focus.) Other immersion liquids have beenproposed, including water with solid particles (e.g. quartz) suspendedtherein.

However, submersing the substrate or substrate and substrate table in abath of liquid (see, for example, U.S. Pat. No. 4,509,852, herebyincorporated in its entirety by reference) means that there is a largebody of liquid that must be accelerated during a scanning exposure. Thisrequires additional or more powerful motors and turbulence in the liquidmay lead to undesirable and unpredictable effects.

One of the solutions proposed is for a liquid supply system to provideliquid on only a localized area of the substrate and in between thefinal element of the projection system and the substrate using a liquidconfinement system (the substrate generally has a larger surface areathan the final element of the projection system). One way which has beenproposed to arrange for this is disclosed in PCT patent applicationpublication WO 99/49504, hereby incorporated in its entirety byreference. As illustrated in FIGS. 2 and 3, liquid is supplied by atleast one inlet IN onto the substrate, preferably along the direction ofmovement of the substrate relative to the final element, and is removedby at least one outlet OUT after having passed under the projectionsystem. That is, as the substrate is scanned beneath the element in a −Xdirection, liquid is supplied at the +X side of the element and taken upat the −X side. FIG. 2 shows the arrangement schematically in whichliquid is supplied via inlet IN and is taken up on the other side of theelement by outlet OUT which is connected to a low pressure source. Inthe illustration of FIG. 2 the liquid is supplied along the direction ofmovement of the substrate relative to the final element, though thisdoes not need to be the case. Various orientations and numbers of in-and out-lets positioned around the final element are possible, oneexample is illustrated in FIG. 3 in which four sets of an inlet with anoutlet on either side are provided in a regular pattern around the finalelement.

SUMMARY

A significant cause of defects in devices manufactured using immersionlithographic apparatus can be bubbles in the immersion liquid, which cancause dose variations and image distortions, depending on the size andlocation of the bubble. It is therefore highly desirable to preventbubbles entering the path of the projection beam. Major sources ofbubbles can be gaps in the smooth top surface of the substrate table(mirror block), for example around sensor units, fiducial plates and thesubstrate. As such gaps pass the liquid supply system (liquidconfinement structure) they may not fill completely and the gas leftbehind may form bubbles. Those bubbles may then rise out of the gap andinto the space between the projection system and the substrate.

Accordingly, it would be advantageous, for example, to provide one ormore arrangements for preventing bubbles formed in a gap in the topsurface of the substrate table from causing imaging defects in theproduction of devices.

According to an aspect of the invention, there is provided alithographic apparatus configured to project an image of a desiredpattern through a liquid onto a substrate held on a substrate table,there being a gap in a surface of the substrate table or between thesubstrate table and another component mounted thereon with which theliquid can, in normal use, come into contact, the gap provided with abubble retaining device configured to retain any bubbles that mightoccur therein.

According to a further aspect of the invention, there is provided alithographic apparatus configured to project an image of a desiredpattern through a liquid onto a substrate held on a substrate table,there being a gap in a surface of the substrate table or between thesubstrate table and another component mounted thereon with which theliquid can, in normal use, come into contact, the gap being dividedalong its length into a plurality of segments.

According to a further aspect of the invention, there is provided alithographic apparatus configured to project an image of a desiredpattern through a liquid onto a substrate held on a substrate table,there being a gap in a surface of the substrate table or between thesubstrate table and another component mounted thereon with which theliquid can, in normal use, come into contact, the apparatus comprising adevice configured to extract liquid, gas or both from the gap.

According to a further aspect of the invention, there is provided alithographic apparatus configured to project an image of a desiredpattern through a liquid onto a substrate held on a substrate table,there being a gap in a surface of the substrate table or between thesubstrate table and another component mounted thereon with which theliquid can, in normal use, come into contact, the apparatus comprising adevice configured to supply liquid to the gap.

According to a further aspect of the invention, there is provided adevice manufacturing method in which an image of a desired pattern isprojected through a liquid onto a substrate held on a substrate table,there being a gap in a surface of the substrate table or between thesubstrate table and another component mounted thereon with which theliquid can, in normal use, come into contact, comprising extractingliquid, gas, or both from the gap and bubbles in the gap are retainedtherein by a bubble retaining device.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict a liquid supply system for use in a lithographicprojection apparatus;

FIG. 4 depicts another liquid supply system for use in a lithographicprojection apparatus;

FIG. 5 depicts a further liquid supply system for use in a lithographicprojection apparatus;

FIG. 6 depicts a gap between the substrate table and the substrateaccording to an embodiment of the invention;

FIG. 7 depicts a gap between the substrate table and the substrateaccording to another embodiment of the invention;

FIG. 8 depicts a gap between the substrate table and the substrateaccording to another embodiment of the invention;

FIG. 9 depicts a gap between the substrate table and the substrateaccording to another embodiment of the invention;

FIG. 10 depicts a gap between the substrate table and the substrateaccording to another embodiment of the invention;

FIG. 11 depicts a gap between the substrate table and the substrateaccording to another embodiment of the invention;

FIG. 12 depicts a gap between the substrate table and the substrateaccording to another embodiment of the invention;

FIG. 13 depicts a gap between the substrate table and the substrateaccording to another embodiment of the invention; and

FIG. 14 depicts a gap between the substrate table and the substrateaccording to another embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises:

an illumination system (illuminator) IL configured to condition aradiation beam PB (e.g. UV radiation or DUV radiation).

a support structure (e.g. a mask table) MT constructed to support apatterning device (e.g. a mask) MA and connected to a first positionerPM configured to accurately position the patterning device in accordancewith certain parameters;

a substrate table (e.g. a wafer table) WT constructed to hold asubstrate (e.g. a resist-coated wafer) W and connected to a secondpositioner PW configured to accurately position the substrate inaccordance with certain parameters; and

a projection system (e.g. a refractive projection lens system) PLconfigured to project a pattern imparted to the radiation beam PB bypatterning device MA onto a target portion C (e.g. comprising one ormore dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure holds the patterning device in a manner thatdepends on the orientation of the patterning device, the design of thelithographic apparatus, and other conditions, such as for examplewhether or not the patterning device is held in a vacuum environment.The support structure can use mechanical, vacuum, electrostatic or otherclamping techniques to hold the patterning device. The support structuremay be a frame or a table, for example, which may be fixed or movable asrequired. The support structure may ensure that the patterning device isat a desired position, for example with respect to the projectionsystem. Any use of the terms “reticle” or “mask” herein may beconsidered synonymous with the more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more mask tables). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AM for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam PB is incident on the patterning device (e.g., maskMA), which is held on the support structure (e.g., mask table MT), andis patterned by the patterning device. Having traversed the mask MA, theradiation beam PB passes through the projection system PL, which focusesthe beam onto a target portion C of the substrate W. With the aid of thesecond positioner PW and position sensor IF (e.g. an interferometricdevice, linear encoder or capacitive sensor), the substrate table WT canbe moved accurately, e.g. so as to position different target portions Cin the path of the radiation beam PB. Similarly, the first positioner PMand another position sensor (which is not explicitly depicted in FIG. 1)can be used to accurately position the mask MA with respect to the pathof the radiation beam PB, e.g. after mechanical retrieval from a masklibrary, or during a scan. In general, movement of the mask table MT maybe realized with the aid of a long-stroke module (coarse positioning)and a short-stroke module (fine positioning), which form part of thefirst positioner PM. Similarly, movement of the substrate table WT maybe realized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the mask table MT may be connected to ashort-stroke actuator only, or may be fixed. Mask MA and substrate W maybe aligned using mask alignment marks M1, M2 and substrate alignmentmarks P1, P2. Although the substrate alignment marks as illustratedoccupy dedicated target portions, they may be located in spaces betweentarget portions (these are known as scribe-lane alignment marks).Similarly, in situations in which more than one die is provided on themask MA, the mask alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the mask table MT and the substrate table WT are keptessentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the mask table MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the masktable MT may be determined by the (de-)magnification and image reversalcharacteristics of the projection system PL. In scan mode, the maximumsize of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the mask table MT is kept essentially stationaryholding a programmable patterning device, and the substrate table WT ismoved or scanned while a pattern imparted to the radiation beam isprojected onto a target portion C. In this mode, generally a pulsedradiation source is employed and the programmable patterning device isupdated as required after each movement of the substrate table WT or inbetween successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4. Liquid is supplied by two groove inlets IN oneither side of the projection system PL and is removed by a plurality ofdiscrete outlets OUT arranged radially outwardly of the inlets IN. Theinlets IN and OUT can be arranged in a plate with a hole in its centerand through which the projection beam is projected. Liquid is suppliedby one groove inlet IN on one side of the projection system PL andremoved by a plurality of discrete outlets OUT on the other side of theprojection system PL, causing a flow of a thin film of liquid betweenthe projection system PL and the substrate W. The choice of whichcombination of inlet IN and outlets OUT to use can depend on thedirection of movement of the substrate W (the other combination of inletIN and outlets OUT being inactive).

Another immersion lithography solution with a localized liquid supplysystem solution which has been proposed is to provide the liquid supplysystem with a liquid confinement structure which extends along at leasta part of a boundary of the space between the final element of theprojection system and the substrate table. Such a solution isillustrated in FIG. 5. The liquid confinement structure is substantiallystationary relative to the projection system in the XY plane thoughthere may be some relative movement in the Z direction (in the directionof the optical axis). In an embodiment, a seal is formed between theliquid confinement structure and the surface of the substrate. In anembodiment, the seal is a contactless seal such as a gas seal. Such asystem is disclosed in United States patent application publication no.US 2004-0207824 and European patent application publication no. EP1420298, each hereby incorporated in its entirety by reference, andillustrated in FIG. 5.

As shown in FIG. 5, a liquid supply system is used to supply liquid tothe space between the projection system and the substrate. The reservoir10 forms a contactless seal to the substrate around the image field ofthe projection system so that liquid is confined to fill a space betweenthe substrate surface and a final element of the projection system. Thereservoir is formed by a liquid confinement structure 12 positionedbelow and surrounding the final element of the projection system PL.Liquid is brought into the space below the projection system via theinlet 13 and within the liquid confinement structure 12. The liquidconfinement structure 12 extends a little above the final element of theprojection system and the liquid level rises above the final element sothat a buffer of liquid is provided. The liquid confinement structure 12has an inner periphery that at the upper end, in an embodiment, closelyconforms to the shape of the projection system or the final elementthereof and may, e.g., be round. At the bottom, the inner peripheryclosely conforms to the shape of the image field, e.g., rectangularthough this need not be the case.

The liquid is confined in the reservoir by a gas seal 16 between thebottom of the liquid confinement structure 12 and the surface of thesubstrate W. The gas seal is formed by gas, e.g. air, synthetic air, N₂or an inert gas, provided under pressure via inlet 15 to the gap betweenliquid confinement structure 12 and substrate and extracted via firstoutlet 14. The overpressure on the gas inlet 15, vacuum level on thefirst outlet 14 and geometry of the gap are arranged so that there is ahigh-velocity gas flow inwards that confines the liquid.

In a lithographic apparatus, the substrate W is commonly placed upon asubstrate holder, also referred to as a pimple plate or burl table,which sits in a recess, often referred to as a pot hole, in the uppersurface of the substrate table WT. To accommodate variations in the sizeand placement of the substrate W within certain tolerances, the recessis slightly larger than the substrate. Thus, although the recess,substrate holder and substrate have dimensions selected to ensure theupper surface of the substrate is substantially co-planar with the uppersurface of the substrate table, a gap will remain around the edges ofthe substrate. Similarly, certain sensors and fiducials (referencemarkers) that are found on the substrate table are mounted on plates orin blocks that are set into corresponding recesses in the substratetable. Again the recesses are slightly oversize to accommodatevariations in the size of the blocks or plates and to enable the sensorsto be removed for servicing or upgrading, leading to gaps.

Such gaps may be a significant source of bubbles that may enter the beampath and affect imaging. The speed of the substrate table when it ismoved so that the gaps pass under the projection system and the spacefilled with immersion liquid is such that there is often insufficienttime for the gaps to completely fill with immersion fluid. Gas thatremains in the gap forms bubbles that can leave the gap and float upinto the path of the projection beam. There, they can cause imagingdefects such as dose variation and image distortion.

FIG. 6 shows a gap between the substrate table and the substrateaccording to an embodiment of the invention. The gap 22 between thesubstrate holder 21 and the recess 20 in which the substrate W andsubstrate holder 21 sit, is provided with a number of hairs 23 which actas a device to retain bubbles in the gap. The hairs 23 are hydrophobic(i.e. have a contact angle of greater than 90° to the immersion liquid,the contact angle being the angle between the solid-liquid interface andthe liquid-gas interface) and act to trap any bubbles 24 that may formin the gap. The bubbles do no harm when retained in the gap; it is onlyif they break free and float into the beam path that imaging defects maybe caused.

FIGS. 7 to 14 depict arrangements according to other embodiments of theinvention. In the following embodiments, parts that are equivalent toparts shown FIG. 6 are identified by like reference numerals and adetailed description is omitted for conciseness. It will of course beappreciated that features of different embodiments can be combined.Arrangements shown applied to the gap around a substrate may of courseequally be applied to the gap around a sensor block or a fiducial plateand indeed any other gap (including a groove) that there may be on theupper surface of the substrate table.

In the embodiment of FIG. 7, the gap 22 around the edge of the substrateW and the gap 25 around the edge of a sensor block SB are segmented bytransverse walls 26 at convenient positions. When the gaps pass underthe liquid confinement system, liquid flows into the gaps but only fillsthe segment or segments of the gap that are partly under the projectionsystem. Being smaller, these can be filled more quickly and completely,reducing or avoiding the formation of bubbles.

FIG. 8 shows an alternative device for retaining bubbles in the gap. Asshown, one or more sharp edges 27 are provided in the gap 22. Anybubbles 24 will be preferentially attached to the sharp edge or edgeswhich effectively increase the contact angle and should not break freeto enter the beam path.

A further device to retain bubbles is shown in FIG. 9. This comprisesone or more overhanging walls 28 to the gap 22 so that it tapersinwardly and upwardly, trapping bubbles in the gap.

In the embodiment of FIG. 10, a rough coating 29 is provided on one ormore suitable surfaces of the gap. The rough coating has changes ofsurface gradient on the same scale as bubbles and thus locally increasesthe contact angle making the surface hydrophobic even if the material ofthe coating is intrinsically hydrophilic. This again acts to retainbubbles in the gap 22.

In the arrangement shown in FIG. 11, the coating 30, which need not berough, is sufficiently hydrophobic to prevent immersion liquid 11entering the gap at all.

Another approach is shown in FIG. 12. This embodiment comprises a liquidsupply 31 that is controlled to supply liquid to the gap 22 in advanceof it moving under the projection system so that the gap is in effectpre-filled. The filling can be completed in sufficient time to ensurethat no or little gas remains and so there are no or few bubbles thatmight enter the beam path. The liquid that fills the gap is, in anembodiment, the immersion liquid but another liquid may be used instead,such as a denser liquid that is immiscible with the immersion liquid. Toavoid the liquid being blown out of the gap, any gas knife or gasbearing in the liquid confinement system should be reduced orswitched-off, at least locally, as the gap passes under the edge of theliquid confinement system.

FIG. 13 shows a further solution to the problem of bubbles in the gap.Here a liquid and gas extractor 32 is used to ensure a flow that sweepsup any bubbles 24 that may be in gap 22 and removes them before they canfloat up to the beam path. A gas-permeable but liquid-impermeablemembrane can be used across the extractor 32 so that only gas isremoved, reducing the consumption of immersion liquid.

FIG. 14 shows the combination of a liquid supply 31 and extractor 32 toset up a horizontal flow that entrains and removes bubbles. In thisapproach, the surfaces of the gap may be hydrophilic to encourage bubblerelease.

Although water-related terms such as hydrophilic, hydrophobic, humidity,etc. may be used herein, these terms should be understood to encompassthe similar properties for other liquids.

In European patent application publication no. EP 1420300 and UnitedStates patent application publication no. US 2004-0136494, each herebyincorporated in their entirety by reference, the idea of a twin or dualstage immersion lithography apparatus is disclosed. Such an apparatus isprovided with two tables for supporting a substrate. Levelingmeasurements are carried out with a table at a first position, withoutimmersion liquid, and exposure is carried out with a table at a secondposition, where immersion liquid is present. Alternatively, theapparatus has only one table.

In an embodiment, there is provided a lithographic apparatus configuredto project an image of a desired pattern through a liquid onto asubstrate held on a substrate table, there being a gap in a surface ofthe substrate table or between the substrate table and another componentmounted thereon with which the liquid can, in normal use, come intocontact, the gap provided with a bubble retaining device configured toretain any bubbles that might occur therein.

In an embodiment, the bubble retaining device comprises a plurality ofhairs having a contact angle to the liquid higher than 90°. In anembodiment, the bubble retaining device comprises one or more sharpedges. In an embodiment, the bubble retaining device comprises atapering of the gap towards the exterior. In an embodiment, the bubbleretaining device comprises a coating having a contact angle to theliquid higher than 90°. In an embodiment, the coating is rough toincrease the effective contact angle.

In an embodiment, there is provided a lithographic apparatus configuredto project an image of a desired pattern through a liquid onto asubstrate held on a substrate table, there being a gap in a surface ofthe substrate table or between the substrate table and another componentmounted thereon with which the liquid can, in normal use, come intocontact, the gap being divided along its length into a plurality ofsegments.

In an embodiment, there is provided a lithographic apparatus configuredto project an image of a desired pattern through a liquid onto asubstrate held on a substrate table, there being a gap in a surface ofthe substrate table or between the substrate table and another componentmounted thereon with which the liquid can, in normal use, come intocontact, the apparatus comprising a device configured to extract liquid,gas or both from the gap.

In an embodiment, the device configured to extract liquid, gas or bothcomprises a membrane configured to allow gas but not liquid to beextracted from the gap. In an embodiment, the device configured toextract liquid, gas or both further comprises a device configured tosupply liquid to the gap.

In an embodiment, there is provided a lithographic apparatus configuredto project an image of a desired pattern through a liquid onto asubstrate held on a substrate table, there being a gap in a surface ofthe substrate table or between the substrate table and another componentmounted thereon with which the liquid can, in normal use, come intocontact, the apparatus comprising a device configured to supply liquidto the gap.

In an embodiment, there is provided a device manufacturing method inwhich an image of a desired pattern is projected through a liquid onto asubstrate held on a substrate table, there being a gap in a surface ofthe substrate table or between the substrate table and another componentmounted thereon with which the liquid can, in normal use, come intocontact, comprising extracting liquid, gas, or both from the gap andbubbles in the gap are retained therein by a bubble retaining device.

In an embodiment, the bubble retaining device comprises a plurality ofhairs having a contact angle to the liquid higher than 90°. In anembodiment, the bubble retaining device comprises one or more sharpedges. In an embodiment, the bubble retaining device comprises atapering of the gap towards the exterior. In an embodiment, the bubbleretaining device comprises a coating having a contact angle to theliquid higher than 90°. In an embodiment, the coating is rough toincrease the effective contact angle.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm).

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, including refractiveand reflective optical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the invention may take the form of acomputer program containing one or more sequences of machine-readableinstructions describing a method as disclosed above, or a data storagemedium (e.g. semiconductor memory, magnetic or optical disk) having sucha computer program stored therein.

One or more embodiments of the invention may be applied to any immersionlithography apparatus, in particular, but not exclusively, those typesmentioned above and whether the immersion liquid is provided in the formof a bath or only on a localized surface area of the substrate. A liquidsupply system as contemplated herein should be broadly construed. Incertain embodiments, it may be a mechanism or combination of structuresthat provides a liquid to a space between the projection system and thesubstrate and/or substrate table. It may comprise a combination of oneor more structures, one or more liquid inlets, one or more gas inlets,one or more gas outlets, and/or one or more liquid outlets that provideliquid to the space. In an embodiment, a surface of the space may be aportion of the substrate and/or substrate table, or a surface of thespace may completely cover a surface of the substrate and/or substratetable, or the space may envelop the substrate and/or substrate table.The liquid supply system may optionally further include one or moreelements to control the position, quantity, quality, shape, flow rate orany other features of the liquid.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1. A lithographic apparatus configured to project an image of a desiredpattern through a liquid onto a substrate held on a substrate table,there being a gap in a surface of the substrate table or between thesubstrate table and another component mounted thereon with which theliquid can, in normal use, come into contact, the gap provided with abubble retaining device configured to retain any bubbles that mightoccur therein.
 2. The apparatus according to claim 1, wherein the bubbleretaining device comprises a plurality of hairs having a contact angleto the liquid higher than 90°.
 3. The apparatus according to claim 1,wherein the bubble retaining device comprises one or more sharp edges.4. The apparatus according to claim 1, wherein the bubble retainingdevice comprises a tapering of the gap towards the exterior.
 5. Theapparatus according to claim 1, wherein the bubble retaining devicecomprises a coating having a contact angle to the liquid higher than90°.
 6. The apparatus according to claim 5, wherein the coating is roughto increase the effective contact angle.
 7. A lithographic apparatusconfigured to project an image of a desired pattern through a liquidonto a substrate held on a substrate table, there being a gap in asurface of the substrate table or between the substrate table andanother component mounted thereon with which the liquid can, in normaluse, come into contact, the gap being divided along its length into aplurality of segments.
 8. A lithographic apparatus configured to projectan image of a desired pattern through a liquid onto a substrate held ona substrate table, there being a gap in a surface of the substrate tableor between the substrate table and another component mounted thereonwith which the liquid can, in normal use, come into contact, theapparatus comprising a device configured to extract liquid, gas or bothfrom the gap and/or to supply liquid to the gap.
 9. The apparatusaccording to claim 8, wherein the device configured to extract liquid,gas or both comprises a membrane configured to allow gas but not liquidto be extracted from the gap.
 10. The apparatus according to claim 8,wherein the device is configured to extract liquid, gas or both.